Question

Imagine that we chop a continuous laser beam (assumed to be monochromatic at λ₀ = 632.8 nm) into t_p = 0.1 ns pulses, using some sort of shutter with a chop rate 1/t_c = 10 kHz.

(a) Compute the resultant laser bandwidth ∆ν, assuming t_c >> t_p.

(b) How does your answer change if we could chop at 10¹⁵ Hz?

Answer 1

Solution Given That Xo = 632.8 nm - 632.88109 m ste= oins = 1010 Here The Coherence length of laser beam is ДТ.: с. БІ Here C= 8x10 10 m is a velouty of light in vaccum AIc = 3x 109 x 16lo Dlc = 8x102m. band width frequeny (DV) = the attorio DV= 100 HZ Now the line width is Here - AIC = C.Ate - e av so, Avata -0 Vg = w group velocity vp - w - phase velocity - Vg - Up is a) Vq = Vp sw = wo up ko Ako ko

Where w (Angular frequey)= QTU k (propageration consteut), Alto) (to) DV = V (-1/287) DV = x (Dio) - from 020 c (neglect negative sign) DIE I DIO SIC = .c.no - T. Dio (or= ô ) to = c A 1 - doido It is

sro - (632.8x1093% 3x102 - 4.0043584 x 103 3410²2 = 1.3347X1041 Ox-0.01330m on the frequency bandwidth Av=105 HZ DI c = cх Ate DI : cx Bv Ale = 37103 10's Ale = 3x107m Die = 300nm width Now line Axo = To = (632.87109) DIC 3X 107 Dio4.0043584 1103 3x107 410 = 1,3347867106 m Slo= 1334.786 nm

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